Changing (or adding) the ability to use up/down arrow keys like + and - numpad keys in Dope Sheet?

When hovering over the Dope Sheet with the mouse, you can use the + and - numpad keys to zoom in and out of the window – as you can in most window types in Blender.

I would like to re-assign (or at least, add) the ability to use the up and down arrow keys in the Dope Sheet so that they will perform the same function as the + and - numpad keys.

I haven’t been able to figure out how to set this particular shortcut up. I don’t want to override what the + and - numpad keys do across the application; I only want to use the up and down arrow keys for this functionality in the Dope Sheet window type. Any ideas?

Never mind – I figured it out: